1. Field of the Invention
The present invention relates to a functional organic compound and uses thereof, more particularly, to a novel 4-cyanocoumarin derivative useful in photochemical polymerization, dye lasers, and electroluminescent elements (abbreviated as xe2x80x9corganic EL elementsxe2x80x9d, hereinafter).
2. Description of the Prior Art
In a multimedia age, photochemical polymerization has been widely used in many fields without restriction to the field of synthetic resins, and it is now being extensively used in the field of information recordings, including memories (hereinafter referred to as xe2x80x9crecordingsxe2x80x9d) and electronic equipments, such as paints, lithographicplates for printing, printing circuits, and integrated circuits. Photochemical polymerization is a technique for polymerizing polymeric compounds by irradiating light and is roughly classified into (i) photopolymerization that initiates the polymerization of polymeric compounds by directly irradiating them for activation, and (ii) photosensitization polymerization that polymerizes polymeric compounds by irradiating them in the presence of photosensitizes to make them into a growth-active form. In both cases, as characteristic features, the initiation and the suspension of polymerization can be controlled by flashing excited light, and the rate and the degree of polymerization can be easily controlled by appropriately selecting the strength and the wavelength of the light. The photochemical polymerization can be proceeded even at a relatively low temperature because it only requires a lesser energy for initiating polymerization.
As a new development of information recordings such as holography and lithographic plates for printing and due to the advantageous features of photochemical polymerization, photopolymeric compositions, which can be polymerized by irradiating visible light such as those of argon ion lasers, helium/neon lasers, and second harmonics of YAG lasers, are now rapidly in great demand. However, polymeric compounds and polymerization initiators, which are generally incorporated into photopolymeric compositions, absorb ultraviolet rays only, and this inevitably needs photosensitizes as a technical factor when polymerizing the compositions with visible light. In photopolymeric compositions used for information recordings and electronic equipments, polymeric compounds should be used in combination with photosensitizes, polymerization initiators, and binding resins, which can be selected from materials to suite their use. In general, there may be employed a technique for selecting materials other than photosensitizes and then selecting photosensitizes capable of sensitizing the selected polymeric compounds and/or polymerization initiators in such a manner of trial and error.
Desired features needed for photosensitizes are as follows: They should have a relatively-high molecular absorption coefficient in a visible region, sensitize polymeric compounds and polymerization initiators, exert a relatively-high sensitization efficiency, have a satisfactory solubility in both solvents and another compounds to be incorporated, and have a satisfactory stability. Representative examples of such photosensitizes are merocyanine dyes as disclosed in Japanese Patent Kokai No. 151,024/79, cyanine dyes as disclosed in Japanese Patent Kokai No. 29,803/83, stilbene derivatives as disclosed in Japanese Patent Kokai No. 56,403/84, coumarin derivatives as disclosed in Japanese Patent Kokai No. 23,901/88, pyran derivatives as disclosed in Japanese Patent Kokai No. 329,654/94, and methylene blue derivatives as disclosed in Japanese Patent Kokai No. 33,104/89. All of these compounds have both merits and demerits, and there found no photopolymeric compound which comprise various materials and constantly exert the aforesaid characteristic features.
Organic compounds which are sensitive to light, more particularly, those which are capable of emitting light are also useful in the field of dye lasers and electroluminescence.
In the field of dye lasers, as disclosed, for example, by Kaoru IGARASHI in xe2x80x9cShikizal-Kyokai-shixe2x80x9d, Vol. 70, No. 2, pp. 102-111 (1997), since dye laser""s lasing was reported in 1960, compounds, which emit light in a visible region, have been eagerly screened. As the progress of information recording technology, compounds which emit light in a longer wavelength region, and more particularly, in a visible region, have been needed more and more.
In the field of information displays, electroluminescent elements (hereinafter abbreviated as xe2x80x9cEL elementsxe2x80x9d) are now highlighted as a display element for the forthcoming generation. At present, cathode-ray tubes are predominantly used in a larger size of information displays such as computer termini and TV receivers. The cathode-ray tubes, however, have a relatively large mass and weight and a relatively high operation voltage, and this hinders their applicability for commonly used equipments and smaller size of portable ones whose transportability is highly valued. More required are the information displays which are relatively small in size like in a thinner and lighter plain form and which operate at a lower operation voltage and wattage. Due to advantageous features of relatively-low operation voltage and wattage, liquid crystal elements are now commonly used in many fields. However, the information displays using such elements will change in contrast when viewed from different angles, display information clearly only within a specific angle, and require blacklight, resulting in a problem of that they could not be reduced their wattage as much as they are expected. As a display element to overcome these drawbacks, there appeared an electroluminescent element, i.e., an organic EL element.
Organic EL elements are generally luminous elements which have a thin film, containing a luminescent agent and being inserted between a cathode and anode, and which utilize luminescence such as fluorescence or phosphorescence emitted by the luminescent agent in such a manner that a direct current voltage is energized between the cathode and anode to supply positive holes and electrons to the film and to couple the positive holes and electrons together to make the agent into an excited state, and the excited agent returns to the ground state while emitting luminescence. As characteristic features, organic EL elements can be appropriately changed its luminous color tint by selecting an appropriate host luminous agent and varying a guest luminescent agent used together with the host. Depending on the combination of luminous agents as the host and guest, the brightness and the life expectancy of luminescence can possibly be improved by a large margin. It is said that organic EL elements are theoretically excellent luminous-elements because of the following merits: Information displays with such organic EL elements are free of view angles because the elements autonomously emit light, and are low in energy consumption because the elements need no blacklight.
In respect of organic EL elements which emit light in a green-color region, there is a report for improving luminous efficiency by using a luminescent agent as a guest. However, there found no effective luminescent agent usable as a guest in organic EL elements for light in a red-color region. Therefore, the latter is far from emitting a complete red-color luminescence and has a relatively-short life expectancy and poor durability and reliability. For example, organic EL elements, as disclosed in Japanese Patent Kokai No. 60,427/98 and U.S. Pat. No. 4,769,292, can only emit an insufficient brightness and an incomplete red-color emission. Accordingly, conventional organic EL elements would still be problematic in realizing a full color emission.
To supply organic EL elements at a relatively-lower cost, it is essential to explore a luminescent agent which does not intrinsically require doping of a guest luminescent agent in addition to simplify the total structure of the elements and to facilitate the vapor deposition in their processings. Many proposals have been made on luminescent agents used for organic EL elements, however, there found no compound which fulfills the aforesaid requirements.
In view of the foregoing, the object of the present invention is to provide a novel organic compound which has a distinct sensitivity to a visible light and a relatively-high luminescent ability, and its uses in photochemical polymerization, organic EL elements, and dye lasers.
To attain the above object, the present inventors eagerly screened compounds and found that a series of 4-cyanocoumarin derivatives, which are obtainable by cyanizing coumarin compounds having a julolidine structure intramolecularly, are highly susceptible to visible light and extremely useful in photochemical polymerization. They also found that the 4-cyanocoumarin derivatives exert a distinct luminescent ability in a visible region and can be advantageously used in dye lasers and organic EL elements. The present invention was made based on the preparation of the novel 4-cyanocoumarin derivatives and the finding of their industrially useful properties.
The present invention solves the above object by providing the novel 4-cyanocoumarin derivatives.